This is a new project that builds on our 15-years of experience studying children with congenital unilateral brain injury. This project will focus on variations in the timing and nature of brain injury, in three experimental groups that have been excluded from our past research on pediatric brain injury: (1) children with late-onset unilateral brain damage, (2) children with early-onset bilateral damage, and (3) children with slow-growing unilateral lesions (tumors). We propose to use both standardized and experimental measures to assess delay,, deviance, recovery and developmental trajectories in language, spatial ability, memory, executive function, and attention, as well as temporal processing ability in language, spatial processing ability, memory, executive function, and attention, as well as temporal processing ability in language, spatial processing and spatial attention. Based on pilot findings and on our previous research with early unilateral brain damage we predict that there will be specific differences in profiles of development for the three groups proposed here. Children with later-onset unilateral lesions are expected to exhibit more deficits in all domains than children with congenital lesions. Subjects with bilateral damage are predicted to demonstrate significant dissociations between language and non-verbal cognitive functions. Children with brain tumors are expected to differ from the other groups because of the slowly evolving nature of their lesions, and to demonstrate more site-specific deficits within the brain. By studying these three groups, and comparing their performance to children with early unilateral brain damage, we can better define the nature and limits of neural specialization of these aspects of language, attention, and non-verbal cognition, and conversely, the nature and limits of neural and behavioral plasticity.